Arc starting electrode



Jan. 6, 1942. K. MARSHALL ARC STARTING ELECTRODE Filed May 6, 1939 INVENTOR.

M K .04 E

M U Y A B Patented Jan. 6, 1942 ARC. STARTING ELECTRODE Laurence K. Marshall, Cambridge, Mass, assignorto Raytheon Manufacturing Company, Newton, Mass, a-corporation of Delaware Application May 6, 1939, Serial No. 27-23202 12' Claims.

This invention relates to a novel igniting-electrode arrangement for starting an are spot on a pool type cathode. The igniting electrode is preferably of the type which is separated by an insulating wall from the cathode, and initiates an are by means of a high voltage impressed between the cathode and the igniting electrode.

An object of this invention is to devise an arc-starting. electrode arrangement wherein the sensitivity and the reliability of said arrangement are substantially increased.

Another object is to lengthen the useful life of such an arrangement.

The foregoing and other objectsof this invention will be best understood from the following description of an exempliflcation thereof, reference being had to the accompanying drawing, wherein:

Fig. 1 is a cross-section of a tube embodying my invention, together with a diagrammatic representation of a circuit with which said tube may be used; and

Fig. 2 is a cross-section taken along. line 2--2 of Fig. 1.

The tube illustrated comprises a sealed envelope I containing a pool cathode 2, preferably consisting of a pool of mercury, and an anode 3-. In order to provide means for initiating an are spot on the surface of the cathode pool 2, the tube is provided with an igniting arrangement 4, consisting of an electrode comprising an elongated conductor 5 separated and insulated from the cathode pool by means of an insulating layer 6 covering the surface of said conductor. This insulating coating or layer is preferably made of glass sealedto the surface of said conductor, preferably as described and claimed in the co-pending application of Percy L. Spencer, Serial No. 251,069; flied January 1 6, 1939, wherein the insulating layer is described as having a thicknessof the order of mils or less. The conductor 5 may be of any convenient diameter, for example between 30 and 40 mils.

The igniting arrangement 4 is floated on the surface of the mercury pool 2 with a considerable length of said igniting electrode in contact with the surface of said pool. Preferably, as illustrated, substantially the entire length of the coated conductor 5 is thus in contact with the surface of said pool. The coated: conductor 5 may be of any convenient shape, as, for example, curved into a ring, as shown more clearly in Fig, 2.

External electrical connection is made to the conductor 5 through a lead-in conductor Tsealed through the bottom wall of the envelope I. A flexible lead 8 connects the upper end of the lead-in conductor 1 to one end of the conductor 5. The lead 8 is of suficient flexibility to permit the coated electrode 5 to float freely on the surface of the pool 2. and to changev its position with variations in the level of saidlpool. As shown, the lead 8 may consist of a light coiled spring. In order to insulate and separate the conductor 1 from the pool 2,, it is covered. by an insulating wall 9,v also preferably of glass. Since it is desired. that theignition occur at the floating igniting structure, the thickness of p the glass layer 9 is preferably made substantially greater than. that. ofthe glass layer 6. I prefer to leave theupper end of the conductor exposed as illustrated. The exposed end of the conductor 1' thus. acts as an electrode which facilitates. the transition of incipient arc spots formed on the surface. of. the pool 2' adjacent the insulating layer 6' into-true arc spots. Furthermore, as soon as such an arc spot is. formed, a discharge occurs between the upper end oftheelectrode l. and the pool 2 which. is ofrelatively low voltage drop. This removes the high. voltage existing between the. conductor. 5' andv thepool' 2. Thus this voltage onlyv rises. tothe value necessary to initiate the. arcspotwhereupon. it is removed.

External electrical connection may be made to the cathode 2 through a lead-in conductor Ill sealed through the lower wall of the envelope I andprojecting into the pool 2. External electrical connectionmay also be made to the anode 3. through. an anode lead-in conductor H sealed. through the upper end of the envelope I.

In tubes of the type described above, the application of a comparatively high voltage between the lead-in. conductors and-I6 will, produce an. incipient cathode spot at some point along the insulating layer '6 in contact with the surface ofthe mercury pool 2. If the anode 3 at such timev has impressed upon it a positive voltage, said incipient are spot will be transformed into a true are. spot which will then be maintainedby said anode.

I have found that if the igniting arrangement is permitted to float on the surface of the pool 2, asvdescribed above, the sensitiveness of the device is substantially increased. Thuslower voltages, applied between the lead-in conductors I and H1, produce more reliable startingof arc spots than in previous devices of this kind. I have found thatv the location at which. the arc spots are initiated is distributed haphazardly'.

I have found that a floating igniting ar.

to excessive values, and also to the distribution of the arc spots along the total length of the insulating layer 6, as described above.

I believe that in prior art devices of this kind, where the location of the incipient arc spots was fixed at a particular spot on the igniting structure, such a spot would become insensitive and no ignition would occur upon the application of the igniting voltage impulse. Thu the occurrence of such an insensitive spot would terminate the useful life of such devices. In my present arrangement, the occurrence of one or more insensitive spots has substantially no effect since there are always a large number of sensitive places along the igniting structure in contact with the mercury surface which are available for the promotion of incipient are spots. The production of punctures through the insulating layer may produce a substantial short-circuiting of the igniting voltage impulses, but insensitive spots do not have this effect. My arrangement, due to the limitation of the magnitude of the i niting voltage impulses, also decreases the tendency for punctures to occur.

Of course it is to be understood that this invention is not limited to the particular arrangementas described above as many equivalents will suggest themselves to those skilled in the art. Various other forms of the igniting electrode structure could be devised. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An arc discharge device comprising an anode, aliquid pool cathode, and an igniting element comprising a conductor insulated from said pool by an insulating wall on said conductor, said igniting element being floated on the surface of said pool with said insulating wall in contact with the surface of said pool.

2. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting element comprising a conductor insulated from said pool by an insulating wall on said conductor, the

weight of said conductor and insulating wall being of a value to cause said conductor and insulating wall to float on the surface of said pool, and a lead-in arrangement for said igniting element constructed to allow said conductor and insulating wall to float on said pool surface.

3. An arc discharge device comprising an anode, a liquidpool cathode, and an igniting element contacting the surface of said pool, the area of said pool socontacted having one dimension of a substantially greater order of magnitude than the other dimension so that an elongated line of contact is established between said element and said pool along which cathode arc spots are initiated, said element being floated on the surface of said pool.

4.. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting electrode provided with an insulating wall contacting the surface of said pool and having a line of contact between said insulating wall and said ment contacting the surface of said pool, the area of said pool so contacted having one dimension of a substantially greater order of magnitude than the other dimension so that an elongated line of contact is established between said element and said pool along which cathode arc spots are initiated, said element being floated on the surface of said pool to maintain said elongated line of contact during operation, whereby said are I spots are distributed along said line of contact.

6. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting elementcomprising an elongated conductor in- I sulated from said pool by an insulating wall on said conductor along a substantial length of said conductor, said igniting element being floated on the surface of said pool with a substantial length of said insulating wall in contact with the surface of said pool.

'7. An arc discharge device comprising a anode, a liquid pool'cathode, and an igniting element comprising a conductor insulated from said pool by an insulating wall on said conductor, the weight of said conductor and insulating wall being of a value to cause said conductor and insulating wall to float on the surface of said pool, a lead-in conductor for said conductor, and a flexible lead connecting said lead-in conductor to said conductor.

8. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting element comprising a conductor insulated from said pool by an insulating wall on said conductor, the weight of said conductor and insulating wall being of a value to cause said conductor and insulating Wall to float on the surface of said pool, a lead-in conductor for said conductor, and a light spring connecting said lead-in conductor to said conductor.

anode, a liquid pool cathode, and an igniting element comprising a conductor insulated from said stituting substantially the sole means for floating said element.

10. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting element comprising a conductor insulated from said pool by an insulating wall on said conductor, the weight of said conductor and insulating wall being of a value to cause said conductor and insulating wall to float on the surface of said pool, said insulating wall constituting substantially the sole means for floating said element.

11. An arc discharge device comprising an anode,'a liquid pool cathode, and an elongated igniting element comprising a conductor insulated from said pool by an insulating wall on said conductor, said igniting element being floated on the surface of said pool with said insulating wall in contact with the surface of said pool. r

12. An arc discharge device comprisingan anode, a liquid pool cathode, and an elongated igniting electrode provided with an. ..insulating wall contacting the surface of said pool and having a line of contact between said insulating wall and said pool along which cathode arc spots are initiated, said electrode and insulating wall being floated on the surface of said pool.

LAURENCE K. MARSHALL. 

